I didn't read Dave's argument that way -- I think he was agreeing with others of us that there's no "48 hour" or "24 hour" advance requirement to have a reservation be honored. If the system allows the reservation, it should be honored, period. If the location has no cars nor intent to get them, they must ensure the system doesn't allow the reservation to be made.

There is a program where some elite members can make a reservation at a "sold out" location even if regular folks can't -- THAT has a 24/48 hour advance requirement.